Study finds common brain organization among disparate mammals
Matthias Kaschube, a lecturer in physics and the Lewis-Sigler Institute for Integrative Genomics at Princeton University, published results of research into the factors determining development of the brain's neural circuits in the Nov. 4 online edition of Science Express.
Kaschube describes his findings as follows:
"In this work we investigated the architecture of a part of the brain involved in visual processing in a diverse set of mammals whose last common ancestor lived 65 million years ago. We found a common design across species that cannot be explained by common descent or common evolutionary pressures."
"The study focuses on the layout of so-called orientation preference maps in the primary visual processing area of the cerebral cortex. These maps reflect the way neural circuits in the brain operate on inputs sent from the retinas as we encounter the features of the visual world around us. They represent all the possible orientations of edges (horizontal, vertical, oblique) that might be present in any one location in what we see. The fundamental unit of structure in these maps that repeats hundreds of times across the visual cortex is called the pinwheel, after the child's toy, because all possible orientations are represented within these modules in a radially symmetric pattern. One signature feature of this common design is the density of pinwheels across the visual area, which turned out to be highly similar across species that are widely separated in evolution."
"The common design is predicted by a mathematical model describing how neural circuits in the brain organize themselves during early visual development. Over the past decades, scientists have worked out for many nonliving systems how mathematics can be used to understand the outcome of a self-organization process. The new results now provide the mathematical concepts needed to obtain such insights for the interplay of neural elements in the visual cortex. The mathematical analysis reveals that a key condition for fixing the emerging neuronal architecture is that nerve cells have the ability to directly signal one another across relatively large distances. Self-organization in different animals can easily generate essentially the same architecture, even if no such architecture was present in any common ancestor."
"The conclusion of this work is that self-organization is at least as important for the development of neural circuits in the brain as the specifications provided by the genome and the accrual of early life experiences. Self-organization must be given greater consideration if we are to understand the forces that shape the emergence of biological characters, including those involved in brain circuits giving rise to complex behavior."
Other researchers involved in the study included Fred Wolf and Michael Schnabel from the Max Planck Institute for Dynamics and Self-Organization, Siegrid Löwel from Göttingen University in Germany, Leonard White from Duke University, and David Coppola from Randolph-Macon College in Ashland, Va.
Funding agencies supporting this work included the National Institutes of Health, the Whitehall Foundation and the National Science Foundation.